A flexible electrochemical biosensor based on functionalized poly(3,4-ethylenedioxythiophene) film to detect lactate in sweat of the human body.

Conductive polymers with good flexibility, conductivity and film-forming ability attract a lot of attention. In this work, a large-area and ordered structure poly(3,4-ethylenedioxythiophene) (PEDOT) film is fabricated at the air-water interface through interface synthesis method. The PEDOT film can be directly placed on a flexible screen-printed electrode, but also has good adhesion between them. The surface of the PEDOT film is relatively smooth, and has good electrical conductivity and flexibility. Lactate oxidase is immobilized on the surface of PEDOT film through a combination of cross-linking and adsorption method to enhance the lactate sensitive performances. The results show that the PEDOT film sensor has excellent stability and reproducibility. The PEDOT film sensor shows a good response to lactate, the working range is 0.25-40 mmol L-1, and the detection limit is 0.083 mmol L-1 (S/N = 3). Moreover, the electrochemical sensor has potential application in detecting lactate in sweat of the human body.

Shape memory of a polymer grating surface fabricated by two-beam interference lithography.

Switchable and reversible optical elements have potential applications in self-adaptive optics. Shape-memory polymer devices with adaptive properties could be easily switched under environment or field stimuli. Here, the laser beam interference technique was used to realize the periodic grating structures of the shape-memory polymer, and memory and recovery of the grating structures were performed. A one-dimensional grating structure was fabricated from dual-beam interference lithography of a nanosecond laser and underwent pressure in a condition of 195°C. The vertical height of the grating was reduced, and the diffraction light was weakened. When the sample was cooled down to room temperature, the morphology of the grating could be kept. After raising the ambient temperature of the sample to 120°C, the morphology of the grating was recovered to the original state, which realized the shape-memory function.

Integration of Multifocal Microlens Array on Silicon Microcantilever via Femtosecond-Laser-Assisted Etching Technology.

Micro-opto-electromechanical systems (MOEMSs) are a new class of integrated and miniaturized optical systems that have significant applications in modern optics. However, the integration of micro-optical elements with complex morphologies on existing micro-electromechanical systems is difficult. Herein, we propose a femtosecond-laser-assisted dry etching technology to realize the fabrication of silicon microlenses. The size of the microlens can be controlled by the femtosecond laser pulse energy and the number of pulses. To verify the applicability of this method, multifocal microlens arrays (focal lengths of 7-9 µm) were integrated into a silicon microcantilever using this method. The proposed technology would broaden the application scope of MOEMSs in three-dimensional imaging systems.

A dual-functional polyaniline film-based flexible electrochemical sensor for the detection of pH and lactate in sweat of the human body.

A flexible dual functional electrochemical sensor based on macroscopic polyaniline (PANI) film is reported. The PANI film is prepared by interfacial synthesis without any additional templates and surfactants, and is easily transferred from the water surface to any substrate. The surface of PANI film is flat and has a certain degree of crystallization. The PANI film exhibits good electrochemical properties, which is attributed to the order structure of PANI. The flexible sensor based on PANI film exhibits good electrochemical performances to pH and lactate. And the flexible PANI sensor has good reproducibility, selectivity and long-term stability. Meanwhile, the PANI sensor is also applied to detect the actual sample (such as food and human sweat), and the results are in accordance with the commercial pH meter, indicating the reliability of the PANI sensor.

Evanescent Field Controllable MZ Sensor via Femtosecond Laser Processing and Mechanic Polishing.

Recently, optical sensors interacting with evanescent fields and the external environment around waveguides have attracted extensive attention. In the process of light propagation in the waveguide, the depth of the evanescent field is closely related to the accuracy of the optical sensor, and adjusting the depth of the evanescent field to obtain higher accuracy has become the primary challenge in fabricating on-chip optical sensors. In this study, the waveguide structure of a Mach-Zehnder interferometer was written directly in Corning Eagle 2000 borosilicate glass by a femtosecond laser, and the sensing window was exposed out of the bulk material by mechanical polishing. The refractive index detection device based on the proposed on-chip Mach-Zehnder interferometer has the advantages of small volume, light weight, and good stability. Its sensitivity can reach 206 nm/RIU or 337 dB/RIU, and the theoretical maximum measurement range is 1-1.508. Therefore, it can measure the refractive index quickly and accurately in extreme or complex environments, and has excellent application prospects.

Trion dynamics and charge photogeneration in MoS2 nanosheets prepared by liquid phase exfoliation.

Since excitonic quasiparticles, including excitons, trions and charges, have a great influence on the photoelectric characteristics of two-dimensional (2D) transition metal dichalcogenides (TMDs), systematic explorations of the trion dynamics and charge photogeneration in 2D TMDs are important for their future optoelectronic applications. Here, broadband femtosecond transient absorption spectroscopic experiments are performed first to investigate the peak shifting and broadening kinetics in MoS2 nanosheets in solution prepared by liquid phase exfoliation (LPE-MoS2, ∼9 layers, 9L), which reveal that the binding energies for the A-, B-, and C-exciton states are ∼77 meV, ∼76 meV, and -70 meV (the energy difference between free charges and excitons; the negative sign for C-excitons means a spontaneous dissociation nature in band-nesting regions), respectively. Then, the trion dynamics and charge photogeneration in LPE-MoS2 nanosheets have been studied in detail, demonstrating that they are comparable to those in chemical vapor deposition grown MoS2 films (1L-, 3L- and 7L-MoS2). These experimental results suggest that LPE-TMD nanosheets also have the potential for use in charge-related optoelectronic devices based on 2D TMDs.

Observation of robust charge transfer under strain engineering in two-dimensional MoS2-WSe2 heterostructures.

Strain is one of the effective ways to modulate the band structure of monolayer transition metal dichalcogenides (TMDCs), which has been reported in theoretical and steady-state spectroscopic studies. However, the strain effects on the charge transfer processes in TMDC heterostructures have not been experimentally addressed thus far. Here, we systematically investigate the strain-mediated transient spectral evolutions corresponding to excitons at band-edge and higher energy states for monolayer MoS2 and monolayer WSe2. It is demonstrated that Γ and K valleys in monolayer WSe2 and monolayer MoS2 present different strain responses, according to the broadband femtosecond pump-probe experimental results. It is further observed that the resulting band offset changes tuned by applied tensile strains in MoS2-WSe2 heterostructures would not affect the band-edge electron transfer profiles, where only monolayer WSe2 is excited. From a flexible optoelectronic applications perspective, the robust charge transfer under strain engineering in TMDC heterostructures is very advantageous.

Many-particle induced band renormalization processes in few- and mono-layer MoS2.

Band renormalization effects play a significant role for two-dimensional (2D) materials in designing a device structure and customizing their optoelectronic performance. However, the intrinsic physical mechanism about the influence of these effects cannot be revealed by general steady-state studies. Here, band renormalization effects in organic superacid treated monolayer MoS2, untreated monolayer MoS2and few-layer MoS2are quantitatively analyzed by using broadband femtosecond transient absorption spectroscopy. In comparison with the untreated monolayer, organic superacid treated monolayer MoS2maintains a direct bandgap structure with two thirds of carriers populated at K valley, even when the initial exciton density is as high as 2.05 × 1014cm-2(under 400 nm excitations). While for untreated monolayer and few-layer MoS2, many-particle induced band renormalizations lead to a stronger imbalance for the carrier population between K and Q valleys inkspace, and the former experiences a direct-to-indirect bandgap transition when the initial exciton density exceeds 5.0 × 1013cm-2(under 400 nm excitations). Those many-particle induced band renormalization processes further suggest a band-structure-controlling method in practical 2D devices.

Micro-/Nano-Structures Fabricated by Laser Technologies for Optoelectronic Devices.

Due to unique optical and electrical properties, micro-/nano-structures have become an essential part of optoelectronic devices. Here, we summarize the recent developments in micro-/nano-structures fabricated by laser technologies for optoelectronic devices. The fabrication of micro-/nano-structures by various laser technologies is reviewed. Micro-/nano-structures in optoelectronic devices for performance improvement are reviewed. In addition, typical optoelectronic devices with micro-nano structures are also summarized. Finally, the challenges and prospects are discussed.

Bioinspired Surfaces With Switchable Wettability.

The surface wettability of plants exhibits many unique advantages, which enhances the environmental adaptability of plants. In view of the rapid development of responsive materials, smart surfaces have been explored extensively to regulate surface wettability through external stimuli. Herein, we summarized recent advancements in bioinspired surfaces with switchable wettability. Typical bioinspired surfaces with switchable wettability and their emerging applications have been reviewed. In the end, we have discussed the remaining challenges and provided perspective on future development.

Time-Resolved Luminescence Properties of Laser-Fabricated Nano-diamonds.

In the study, well-crystallized nano-diamonds with an average size of 3.8 nm are obtained via femtosecond laser ablation. Both steady-state and transient luminescence are observed. The luminescence peaks of nano-diamonds shift from 380 to 495 nm when the excitation wavelength changes from 280 to 420 nm. After passivation by polyethylene glycol-400N, the surface of nano-diamonds is significantly oxidized, which is verified by Raman and UV-Vis absorption spectra. Furthermore, there is no change in all the luminescence wavelengths, although the maximum intensity increases by 10 times. Time-resolved luminescence spectra reveal that trapping states can be modified by surface passivation, and this leads to stronger luminescence with a longer lifetime.

Periodic Microstructures Fabricated by Laser Interference with Subsequent Etching.

Periodic nanostructures have wide applications in micro-optics, bionics, and optoelectronics. Here, a laser interference with subsequent etching technology is proposed to fabricate uniform periodic nanostructures with controllable morphologies and smooth surfaces on hard materials. One-dimensional microgratings with controllable periods (1, 2, and 3 µm) and heights, from dozens to hundreds of nanometers, and high surface smoothness are realized on GaAs by the method. The surface roughness of the periodic microstructures is significantly reduced from 120 nm to 40 nm with a subsequent inductively coupled plasma (ICP) etching. By using laser interference with angle-multiplexed exposures, two-dimensional square- and hexagonal-patterned microstructures are realized on the surface of GaAs. Compared with samples without etching, the diffraction efficiency can be significantly enhanced for samples with dry etching, due to the improvement of surface quality.

PL Tunable GaN Nanoparticles Synthesis through Femtosecond Pulsed Laser Ablation in Different Environments.

The tunable photoluminescence (PL) property is very important for gallium nitride (GaN) nanoparticles in the application of ultraviolet and blue optoelectronic devices, while conventional methods are not so satisfactory that alternative methods for preparing GaN nanoparticles should be studied. In this paper, ultra-small and well dispersed GaN nanoparticles are fabricated through femtosecond pulse laser ablation in air, water and ethanol. For the PL spectra of GaN nanoparticles, there are no shifts in air, red shifts in water and blue shifts in ethanol compared with the intrinsic PL spectra of bulk GaN. The X-ray photoelectron spectroscopy (XPS) results demonstrate that the various PL spectra can be due to the different components inside the GaN nanoparticles, which not only have effect on the PL emissions, but also greatly influence the intensity of PL. This study validates that the ablation environment has a great adjustable effect on the properties of GaN nanoparticles.

Transient Depolarization Spectroscopic Study on Electronic Structure and Fluorescence Origin of Graphene Oxide.

It is well-established that the electronic states of graphene oxide (GO) consist of sp2 clusters with different sizes and the surrounding sp3 matrix according to recent reports. However, addressing the excitation energy migration/redistribution among those electronic states in GO-based complex systems from spectroscopic experiments is still a challenge. Here, we combine the time-resolved absorption and fluorescence depolarization experiments to reveal the excitation energy migration processes in electronic states in GO. We demonstrate that, in sp3 domains of GO, there are charge-transfer states between sp3-hybridized carbon atoms and the oxygen-containing functional groups, and the energy redistribution and charge migration in sp3 matrix occur on the time scale from subpicoseconds to tens of picoseconds. In contrast, the electronic states of sp2 clusters in GO are rather localized and dominantly contribute to the excitation-wavelength-dependent red fluorescence of GO.

Mechanism of Triplet Energy Transfer in Photosynthetic Bacterial Reaction Centers.

In purple bacterial reaction centers, triplet excitation energy transfer occurs from the primary donor P, a bacteriochlorophyll dimer, to a neighboring carotenoid to prevent photodamage from the generation of reactive oxygen species. The BB bacteriochlorophyll molecule that lies between P and the carotenoid on the inactive electron transfer branch is involved in triplet energy transfer between P and the carotenoid. To expand the high-resolution spectral and kinetic information available for describing the mechanism, we investigated the triplet excited state formation and energy transfer pathways in the reaction center of Rhodobacter sphaeroides using pump-probe transient absorption spectroscopy over a broad spectral region on the nanosecond to microsecond time scale at both room temperature and at 77 K. Wild-type reaction centers were compared with a reaction center mutant (M182HL) in which BB is replaced by a bacteriopheophytin (Φ), as well as to reaction centers that lack the carotenoid. In wild-type reaction centers, the triplet energy transfer efficiency from P to the carotenoid was essentially unity at room temperature and at 77 K. However, in the M182HL mutant reaction centers, both the rate and efficiency of triplet energy transfer were decreased at room temperature, and at 77 K, no triplet energy transfer was observed, attributable to a higher triplet state energy of the bacteriopheophytin that replaces bacteriochlorophyll in this mutant. Finally, detailed time-resolved spectral analysis of P, carotenoid, and BB (Φ in the M182HL mutant) reveals that the triplet state of the carotenoid is coupled fairly strongly to the bridging intermediate BB in wild-type and Φ in the M182HL mutant, a fact that is probably responsible for the lack of any obvious intermediate 3BB/3Φ transient formation during triplet energy transfer.

Size-dependent one-photon- and two-photon-pumped amplified spontaneous emission from organometal halide CH3NH3PbBr3 perovskite cubic microcrystals.

In the past few years, organometal halide light-emitting perovskite thin films and colloidal nanocrystals (NCs) have attracted significant research interest in the field of highly purified illuminating applications. However, knowledge of photoluminescence (PL) characteristics, such as amplified spontaneous emission (ASE) of larger-sized perovskite crystals, is still relatively scarce. Here, we presented room-temperature size-dependent spontaneous emission (SE) and ASE of the organometal halide CH3NH3PbBr3 perovskite cubic microcrystals pumped through one-photon-(1P) and two-photon-(2P) excitation paradigms. The results showed that the optical properties of SE and ASE were sensitively dependent on the sizes of perovskite microcrystals irrespective of whether 1P or 2P excitation was used. Moreover, by comparing the spectral results of 1P- and 2P-pumped experiments, 2P pumping was found to be an effective paradigm to reduce thresholds by one order of magnitude. Finally, we carried out fluences-dependent time-resolved fluorescence dynamics experiments to study the underlying effects of these scale-dependent SE and ASE. We found that the photoluminescence (PL) recombination rates sensitively became faster with increasing carriers' densities, and that the ASE pumped from larger-sized CH3NH3PbBr3 perovskite cubic microcrystals showed faster lifetimes. This work shows that micro-sized perovskite cubic crystals could be the ideal patterns of perovskite materials for realizing ASE applications in the future.

The Role of Trap-assisted Recombination in Luminescent Properties of Organometal Halide CH3NH3PbBr3 Perovskite Films and Quantum Dots.

Hybrid metal halide perovskites have been paid enormous attentions in photophysics research, whose excellent performances were attributed to their intriguing charge carriers proprieties. However, it still remains far from satisfaction in the comprehensive understanding of perovskite charge-transport properities, especially about trap-assisted recombination process. In this Letter, through time-resolved transient absorption (TA) and photoluminescence (PL) measurements, we provided a relative comprehensive investigation on the charge carriers recombination dynamics of CH3NH3PbBr3 (MAPbBr3) perovskite films and quantum dots (QDs), especially about trap-assisted recombination. It was found that the integral recombination mode of MAPbBr3 films was highly sensitive to the density distribution of generated charge carriers and trap states. Additional, Trap effects would be gradually weakened with elevated carrier densities. Furthermore, the trap-assisted recombination can be removed from MAPbBr3 QDs through its own surface passivation mechanism and this specialty may render the QDs as a new material in illuminating research. This work provides deeper physical insights into the dynamics processes of MAPbBr3 materials and paves a way toward more light-harvesting applications in future.

Ultrafast Electron Transfer Kinetics in the LM Dimer of Bacterial Photosynthetic Reaction Center from Rhodobacter sphaeroides.

It has become increasingly clear that dynamics plays a major role in the function of many protein systems. One system that has proven particularly facile for studying the effects of dynamics on protein-mediated chemistry is the bacterial photosynthetic reaction center from Rhodobacter sphaeroides. Previous experimental and computational analysis have suggested that the dynamics of the protein matrix surrounding the primary quinone acceptor, QA, may be particularly important in electron transfer involving this cofactor. One can substantially increase the flexibility of this region by removing one of the reaction center subunits, the H-subunit. Even with this large change in structure, photoinduced electron transfer to the quinone still takes place. To evaluate the effect of H-subunit removal on electron transfer to QA, we have compared the kinetics of electron transfer and associated spectral evolution for the LM dimer with that of the intact reaction center complex on picosecond to millisecond time scales. The transient absorption spectra associated with all measured electron transfer reactions are similar, with the exception of a broadening in the QX transition and a blue-shift in the QY transition bands of the special pair of bacteriochlorophylls (P) in the LM dimer. The kinetics of the electron transfer reactions not involving quinones are unaffected. There is, however, a 4-fold decrease in the electron transfer rate from the reduced bacteriopheophytin to QA in the LM dimer compared to the intact reaction center and a similar decrease in the recombination rate of the resulting charge-separated state (P(+)QA(-)). These results are consistent with the concept that the removal of the H-subunit results in increased flexibility in the region around the quinone and an associated shift in the reorganization energy associated with charge separation and recombination.

Elucidating the band structure and free charge carrier dynamics of pure and impurities doped CH3NH3PbI(3-x)Cl(x) perovskite thin films.

CH3NH3PbI3-xClx perovskite material has been commonly used as the free charge generator and reservoir in highly efficient perovskite-based solid-state solar photovoltaic devices. However, many of the underlying fundamental photophysical mechanisms in this material such as the perovskite transition band structure as well as the dependent relationship between the carrier properties and lattice properties still lack sufficient understanding. Here, we elucidated the fundamental band structure of the pure CH3NH3PbI3-xClx pervoskite lattice, and then reported about the dependent relationship between the free charge carrier characteristic and the different CH3NH3PbI3-xClx pervoskite lattice thin films utilizing femtosecond time-resolved pump-probe technologies. The data demonstrated that the pure perovskite crystal band structure should only have one conduction and one valence band rather than dual valences, and the pure perovskite lattice could trigger more free charge carriers with a slower recombination rate under an identical pump intensity compared with the impurities doped perovskite crystal. We also investigated the perovskite film performance when exposed to moisture and water, the corresponding results gave us a dip in the optimization of the performance of perovskite based devices, and so as a priority this material should be isolated from moisture (water). This work may propose a deeper perspective on the comprehension for this material and it is useful for future optimization of applications in photovoltaic and light emission devices.

Synthesized Blue Fluorescent Protein Analogue with Tunable Colors from Excited-State Intramolecular Proton Transfer through an N-H···N Hydrogen Bond.

A synthesized blue fluorescent protein (BFP) chromophore analogue 2-BFP ((4Z)-4-[(1H-imidazol-2-yl)methylene]-1-methyl-2-phenyl-1H-imidazol-5(4H)-one) displays dual fluorescent emission that arises from the same Z-isomer. The larger Stokes shift emission is a result of excited-state intramolecular proton transfer (ESIPT) mediated by an N-H···N type of hydrogen bond. Compared to other green fluorescent protein (GFP) analogues with ESIPT such as o-HBDI, 2-BFP possesses greatly enhanced quantum yields and much slower proton-transfer rates. In addition, fluorescence up-conversion experiments revealed two rising components of lifetime for the tautomer formation of 2-BFP. The results imply that the relaxation of the N* state in 2-BFP triggers the proton transfer of the molecule. The weaker photoacidity of N-H is proposed to be crucial for these photophysical and photochemical properties. Finally, the ESIPT process in 2-BFP is inhibited in protic solvents (MeOH) or by the formation of metal-chelate complexes, providing insights for further developments and applications of ESIPT molecules.